Question

We are getting an error in a VB6 application that sends data back and forth over TCP sockets. We get a runtime error ‘out of string space’. Has anyone seen this or have any thoughts on why this would happen? It seems like we are hitting some VB6 threshhold so any other thoughts would be helpful as well.

Answer 1

As others have pointed out, every string concatenation in VB will allocate a new string and then copy the data over and then de-allocate the original once it can. In a loop this can cause issues.

To work around this you can create a simple StringBuilder class like this one:

Option Explicit  Private data As String Private allocLen As Long Private currentPos As Long  Public Function Text() As String   Text = Left(data, currentPos) End Function  Public Function Length() As Long   Length = currentPos End Function  Public Sub Add(s As String)    Dim newLen As Long   newLen = Len(s)   If ((currentPos + newLen) > allocLen) Then     data = data & Space((currentPos + newLen))     allocLen = Len(data)   End If    Mid(data, currentPos + 1, newLen) = s   currentPos = currentPos + newLen  End Sub  Private Sub Class_Initialize()   data = Space(10240)   allocLen = Len(data)   currentPos = 1 End Sub 

This class will minimize the number of string allocations by forcing the string to be built with spaces in it and then overwriting the spaces as needed. It re-allocates to roughly double its size when it finds that it does not have enough space pre-initialized. The Text method will return the portion of the string that is actually used.